Bump django-environ from 0.3.0 to 0.8.1

Bumps [django-environ](https://github.com/joke2k/django-environ) from 0.3.0 to 0.8.1.
- [Release notes](https://github.com/joke2k/django-environ/releases)
- [Changelog](https://github.com/joke2k/django-environ/blob/main/CHANGELOG.rst)
- [Commits](joke2k/django-environ@v0.3...v0.8.1)

---
updated-dependencies:
- dependency-name: django-environ
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,6 +1,6 @@
 coverage==3.7.1
 Django==1.8.3
-django-environ==0.3.0
+django-environ==0.8.1
 gunicorn==19.3.0
 httplib2==0.9.1
 pbr==1.3.0